My friend sent me this and asked me what the value printed at the end is, which promise would win the race.

const promise1 = new Promise((resolve) => {
  for (let i = 0; i < 10000; i++) {} // longer loop
  resolve('promise1');
});

const promise2 = new Promise((resolve) => {
  for (let i = 0; i < 100; i++) {} // shorter loop
  resolve('promise2');
});

Promise.race([promise1, promise2]).then((value) => console.log(value));

Surprisingly, most of their answers are the same, with promise2 to be printed at the end!

If you have been working with Nodejs long enough and understand its event loop, you can immediately see the problem in the above code. Even though the code is inside a Promise, which should be run concurrently (in normal mindset). However, the for loops contain nothing inside. They are called blocking code in js. Since Nodejs is single-threaded, the above functions will be executed sequentially, in the order of declaration.

It will behave differently only when you add some non-blocking (async) operation inside the Promise, for example setInterval.

Turns out a lot of them also use ChatGPT to get the answer 🥸

In conclusion, use these AIs to speed up and improve your workflow, but don’t completely trust them. Always verify the answers yourself.